The field of application of the invention is in particular that of gas turbine aeroengines. Nevertheless, the invention is applicable to other turbine engines, e.g. industrial turbines.
Ceramic matrix composite (CMC) materials are known for conserving their mechanical properties at high temperatures, which makes them suitable for constituting hot structural elements.
In gas turbine aeroengines, improving efficiency and reducing certain polluting emissions both lead to seeking to obtain operation at ever higher temperatures. For turbine ring assemblies that are made entirely out of metal, it is necessary to cool all of the elements of the assembly, and in particular the turbine ring, which is subjected to very hot streams, typically at temperatures higher than those that can be withstood by the metal material. Such cooling has a significant impact on the performance of the engine, since the cooling stream that is used is taken from the main stream through the engine. In addition, the use of metal for the turbine ring limits potential for increasing temperature in the turbine, even though that would enable the performance of aeroengines to be improved.
Furthermore, a metal turbine ring assembly deforms under the effect of temperature variations, thereby modifying clearances for the flow passage, and consequently modifying the performance of the turbine.
That is why proposals have already been made to use CMC for various hot portions of engines, particularly since CMC presents the additional advantage of density that is lower than the density of the refractory metals that are conventionally used.
Thus, making turbine ring sectors as a single piece of CMC is described in particular in Document US 2012/0027572. Ring sectors comprise an annular base with an inner face defining the inside face of the turbine ring and an outer face from which there extend two tab-forming portions with their ends engaged in housings in a metal ring support structure.
The use of CMC ring sectors makes it possible to reduce significantly the amount of ventilation that is needed for cooling the turbine ring. Nevertheless, holding ring sectors in position remains a problem, in particular in the face of differential expansions that can occur between the metal support structure and the CMC ring sectors. That is why it is necessary to provide a certain minimum amount of clearance between the assembled parts. Unfortunately, such clearance degrades good control over the shape of the passage and also the behavior of ring sectors in the event of contacting the tips of blades of the turbine. In addition, the presence of such clearance leads to problems with vibration.